What would it taste like if I added some into the keg in a hop bag... dry hopped it a few days? Just out of curiosity.

Weird. It'd be a too sweet banana hefe with hops flavor. Hops flavor and/or aroma is out of place in a hefeweizen and would compete with the banana and cloves that are the trademark of a hefeweizen.

Keep in mind that carbing changes the level of perceived sweetness in a beer! The carbonic acid from carbonation gives a perception of less sweetness. That may be enough to make the beer very drinkable!

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